got 5 single conductor #10 thwn wires in conduit...colors are red,black,white,white,green. distance is 650 feet,one way. voltage is 120v/1-phase...feeding two security lights...each pulling 3.0(three)amps. vd calculator says 4.7 volts dropped or 3.9%....question: should I use one white as the neutral for both hot conductors and keep the other white for a spare or should I use a seperate white neutral for each hot conductor?
voltage drop
- Thread starter wildman
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Re: voltage drop
Use one white and create a multi-wire circuit.
To see why, calculate VD and I^2R loss both ways, ((1) multi-wire circuit and (2) two wire circuits) and see which method is more efficient.
Roger
[ November 20, 2003, 07:10 PM: Message edited by: roger ]
Use one white and create a multi-wire circuit.
To see why, calculate VD and I^2R loss both ways, ((1) multi-wire circuit and (2) two wire circuits) and see which method is more efficient.
Roger
[ November 20, 2003, 07:10 PM: Message edited by: roger ]
Re: voltage drop
thanks roger....correct me if I am wrong in my reasoning......using two neutrals each will read 3.0 amps....3.0 amps on the hot conductor and 3.0 amps on the return (neutral)the vd would be the same on each conductor.....using only one neutral...the unbalance load from the two hot conductors would be zero current...3.0 amps minus 3.0 amps.....zero current equals no vd on the neutral conductor!
thanks roger....correct me if I am wrong in my reasoning......using two neutrals each will read 3.0 amps....3.0 amps on the hot conductor and 3.0 amps on the return (neutral)the vd would be the same on each conductor.....using only one neutral...the unbalance load from the two hot conductors would be zero current...3.0 amps minus 3.0 amps.....zero current equals no vd on the neutral conductor!
G
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Re: voltage drop
Wouldn't there be even less voltage drop on the neutral if both whites were used in the multi-wire circuit example?
Wouldn't there be even less voltage drop on the neutral if both whites were used in the multi-wire circuit example?
hurk27
Senior Member
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- Portage, Indiana NEC: 2008
Re: voltage drop
Huh?
Awwt read 300.4
[ November 20, 2003, 11:50 PM: Message edited by: hurk27 ]
Huh?
Awwt read 300.4
[ November 20, 2003, 11:50 PM: Message edited by: hurk27 ]
david
Senior Member
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- Pennsylvania
Re: voltage drop
Wildman:
The above statement leads me to believe this is an existing pull, or are you the one making this pull? I don?t want to assume you researched this and determined that the black phase and the red phase are not already part of a multi-wire circuit.
Wildman:
The above statement leads me to believe this is an existing pull, or are you the one making this pull? I don?t want to assume you researched this and determined that the black phase and the red phase are not already part of a multi-wire circuit.
Re: voltage drop
I think hurk meant 310.4 rather than 300.4. I think the intent of that section is to prohibit paralleling conductors smaller than 1/0 unless one of the exceptions apply. As written however, that section doesn't really do what I think it is meant to do. It says conductors 1/0 and larger shall be permitted to be connected in parallel. It doesn't say smaller conductors shall not be permitted to be connected in parallel If the code doesn't prohibit it, doesn't that mean it's ok?
I think hurk meant 310.4 rather than 300.4. I think the intent of that section is to prohibit paralleling conductors smaller than 1/0 unless one of the exceptions apply. As written however, that section doesn't really do what I think it is meant to do. It says conductors 1/0 and larger shall be permitted to be connected in parallel. It doesn't say smaller conductors shall not be permitted to be connected in parallel
If the code doesn't prohibit it, doesn't that mean it's ok?
G
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Re: voltage drop
Exactly right-- parallel. And I'm thowing it out here as a physics issue, not an NEC issue.
G
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Re: voltage drop
Originally posted by hurk27:
Huh?
[Edit add to clarify this post. Things are hectic here today and I did not refresh before posting, so I missed the clarification from eprice. Thanks eprice! I'll go read 310.4 now.]
[ November 21, 2003, 08:52 PM: Message edited by: awwt ]
- Location
- Lockport, IL
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- Retired Electrical Engineer
Re: voltage drop
Speaking only from the perspective of physics, Wayne is right. The same current going through half the resistance will give you half the voltage drop. That improves the voltage at the load by about 25%. That is, it would reduce a 4% VD to about a 3% VD.
Re: voltage drop
It appears to me that 310.4 does indeed forbid conductors smaller than #1/0 to be paralleled, as indicated by the exceptions. That said, what would be wrong with paralleling #12s on a switch run to some device, provided the branch circuit is protected to 20 amps? Even if one of the parallel branches were lost, there would be no excessive current on any conductor. One would have to contain all conductors in the same raceway or cable, or at least in close proximity to one another to restrict EMF. Comments?
It appears to me that 310.4 does indeed forbid conductors smaller than #1/0 to be paralleled, as indicated by the exceptions. That said, what would be wrong with paralleling #12s on a switch run to some device, provided the branch circuit is protected to 20 amps? Even if one of the parallel branches were lost, there would be no excessive current on any conductor. One would have to contain all conductors in the same raceway or cable, or at least in close proximity to one another to restrict EMF. Comments?
Re: voltage drop
If you can, try to visualize the following schematic:
H____________________________________________H
| |
\___________________________________/
|_____________________________________|
| |
O O
N___|_____________________________________|___N
House Garage
|
\ is a three way switch
|
|
O is a light fixture
|
|___ or __|__ are connections
|
What do you think of the parallel wires under some switching arangements?
This schematic could be used (legally?) for wiring three ways for a light at a garage door, also having a receptacle for the garage, using only 4 wires. Usually, this would require 5 wires, plus ground.
If you can, try to visualize the following schematic:
H____________________________________________H
| |
\___________________________________/
|_____________________________________|
| |
O O
N___|_____________________________________|___N
House Garage
|
\ is a three way switch
|
|
O is a light fixture
|
|___ or __|__ are connections
|
What do you think of the parallel wires under some switching arangements?
This schematic could be used (legally?) for wiring three ways for a light at a garage door, also having a receptacle for the garage, using only 4 wires. Usually, this would require 5 wires, plus ground.
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: voltage drop
I think the difference between allowing the paralleling of large conductors versus not allowing the paralleling of small conductors is that the probability of the conductor being accidentally disconnected (i.e., at a point of termination) or cut (e.g., from being struck) is far lower for the larger, heavier, sturdier conductors. Just a guess.
Presuming you are asking why the NEC forbids it, I cannot say for certain. But I?d wonder why you would want to. If a single #12 can handle the load, why put a pair of #12s in parallel? For one thing, you would have to count each of the #12s as a separate current-carrying conductor, so that Table 310.15(B)(2)(a) might come into play.
I think the difference between allowing the paralleling of large conductors versus not allowing the paralleling of small conductors is that the probability of the conductor being accidentally disconnected (i.e., at a point of termination) or cut (e.g., from being struck) is far lower for the larger, heavier, sturdier conductors. Just a guess.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: voltage drop
Sorry Awwt it was 310.4 I was refering to. as I was thinking that paralleling of wires smaller than 1/O was not allowed.
Sorry Awwt it was 310.4 I was refering to. as I was thinking that paralleling of wires smaller than 1/O was not allowed.
- Location
- Massachusetts
Re: voltage drop
In this case awwts suggestion of paralleling the white wires would be a violation, but of course he knew that.
He was just "thowing it out here as a physics issue". :roll:
I think most of us knew you meant 310.4.
In this case awwts suggestion of paralleling the white wires would be a violation, but of course he knew that.
He was just "thowing it out here as a physics issue". :roll:
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